1. Field of the Invention
This invention generally relates to methods for determining one or more electrical parameters of an insulating film. Certain embodiments relate to methods for imperfect insulating film electrical thickness and/or capacitance measurements.
2. Description of the Related Art
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, insulating (or dielectric) films may be formed on multiple levels of a substrate using deposition processes such as chemical vapor deposition (“CVD”), physical vapor deposition (“PVD”), and atomic layer deposition (“ALD”). In addition, insulating films may be formed on multiple levels of a substrate using a thermal growth process. For example, a layer of silicon dioxide may be thermally grown on a substrate by heating the substrate to a temperature of greater than about 700° C. in an oxidizing ambient such as O2 or H2O. Such insulating films may electrically isolate conductive structures of a semiconductor device formed on the substrate.
Measuring and controlling electrical parameters of insulating films such as capacitance is an important aspect of semiconductor device manufacturing. A number of techniques are presently available for measuring capacitance of insulating films.
One example of a technique that can be used to measure the capacitance of insulating films is the mercury probe CV technique. This technique includes using the mercury probe as an electrode and making physical contact between the probe and the top of the insulating film. A voltage is then applied to the insulating film, and the capacitance of the film is measured. Such measurements have the disadvantages of requiring calibration of the surface contact area, variation of the film thickness in the measurement area due to pressure applied on the surface of the film during measurement, and frequent variations in the mercury probe due to mercury oxidation.
Another technique that can be used to measure the capacitance of insulating films is the MOS Cap CV technique. This technique utilizes a metal or a heavily doped polysilicon (poly-Si) electrode to measure capacitance of insulating films by supplying an electric voltage on the electrode. Such measurements have a long history and established utility, however, the weakness of the measurement is the length of time needed to obtain results. For example, it normally takes a few days to make such conductive electrode measurements. Therefore, such a technique is not suitable for in-line capacitance monitoring in many manufacturing situations.
Non-contacting electrical test methodologies have been developed to provide electrical capacitance, electrical thickness, and electrical conductivity measurements. Non-contact electrical measurement techniques have unique advantages in that no modifications to the surface of the insulating film occur during measurement, no contamination is introduced to the fab due to the measurement, the measurements have excellent stability and repeatability, and the measurements can produce results relatively quickly. These techniques, typically, use a charge generation source such as a corona generator and a non-contacting voltage measurement sensor such as a Kelvin probe or a Monroe probe to determine the electrical properties of the films. Examples of such techniques are illustrated in U.S. Pat. No. 5,485,091 to Verkuil, U.S. Pat. No. 6,097,196 to Verkuil et al., and U.S. Pat. No. 6,202,029 to Verkuil et al., which are incorporated by reference as if fully set forth herein.
A non-contacting pure capacitance and electrical thickness test method for imperfect insulators is described in U.S. patent application Ser. No. 60/394,835 entitled “Methods and Systems for Determining a Property of an Insulating Film,” filed Jul. 10, 2002, which is incorporated by reference as if fully set forth herein. This method includes measuring both capacitance and conduction or leak rate under a given bias to determine the real capacitance and/or electrical thickness of imperfect insulators.